The present invention relates to a wet-type multiplate clutch, and more particularly to a wet-type multiplate clutch comprising a plurality of clutch discs coupled to an engine and a plurality of clutch plates coupled to a wheel, the clutch discs and plates being alternately interleaved so that they can be pressed against and spaced from each other, and also being supplied with cooling oil therebetween.
Generally, clutches selectively transmit drive forces generated by an engine to a wheel and cut off the transmission of drive forces from the engine to the wheel. The clutches are mainly grouped into two types, i.e., a dry-type multiplate clutch and a wet-type multiplate clutch. The wet-type multiplate clutch finds wide use on two-wheeled motor vehicles such as motorcycles which have a relatively small vehicle body weight with respect to the drive force generated by the engine, since the wet-type multiplate clutch does not suffer a large shock when the motorcycle transmission effects a gear shift.
The wet-type multiplate clutch on a motor vehicle comprises a plurality of clutch discs coupled to the engine and a plurality of clutch plates coupled to a wheel, the clutch discs and plates being alternately interleaved and supplied with oil therebetween. The drive forces from the engine can be transmitted to the wheel by pressing the clutch plates against the clutch discs.
FIGS. 1(a) and 1(b) of the accompanying drawings illustrate a conventional clutch disc for use in a wet-type multiplate clutch, disclosed in Japanese Laid-Open Utility Model Publication No. 50-30145. A clutch disc 2 comprises a centrally open disc plate 6 having a plurality of engaging teeth 4 on its outer periphery, with ring shaped frictional members 10 being attached to opposite surfaces of the clutch disc 2. Each of the frictional members 10 has eight radial oil passages 8 defined in one surface thereof at angularly spaced intervals and eight oil grooves 9 (see FIG. 1(b)) of an inverted J-shaped cross section each having one end opening at the inner peripheral surface of the frictional member 10 and the other end closed at the surface of the frictional member 10, the oil passages 8 and oil grooves 9 being alternately arranged as shown in FIG. 1(a).
The clutch disc 2 is rotatable in the direction of the arrow by engagement of the engaging teeth 4 with an outer clutch member (not shown) directly coupled to an engine. When a clutch plate (not shown) is pressed against the clutch disc 2, the clutch disc 2 and the clutch plate are frictionally joined to each other through a frictional surface 11 of the frictional member 10 to transmit the drive forces from the engine to a wheel coupled to the clutch plate. The clutch disc 2 and the clutch plate are partly immersed in oil 12. The oil 12 is discharged into a central region of the clutch by an oil pump (not shown), and forced to flow radially outwardly via the radial oil passages 8 under centrifugal forces produced upon rotation of the clutch disc 2. At the same time, the oil 12 is retained in the oil grooves 9. The oil 12 serves to remove frictional heat generated when the clutch disc 2 and the clutch plate are pressed against each other, and also serves to absorb shocks produced when the clutch disc 2 and the companion clutch plate are engaged and disengaged.
The clutch disc 2 is required to be durable since it is frictionally held against the clutch plate each time a transmission gear shift is effected, and also required to be smoothly pressed against and separated from the clutch plate when the clutch is engaged and disengaged. The increased durability of the clutch disc 2 results in a reduced maintenance cost, and the smooth engagement and disengagement gives rise to improved riding comfort. According to the illustrated prior clutch disc 2, a cooling effect provided by the oil 12 flowing through the oil passage 8 is aimed at increased durability of the clutch disc 2, whereas an oil pressure developed by centrifugal forces acting on the oil 12 retained in the oil grooves 9 is designed to increase smoothness in engaging and disengaging the clutch.
It has however been confirmed by the inventor that the illustrated numbers and shapes of the oil passages 8 and oil grooves 9 are not sufficient to provide a desired cooling effect and oil pressure. More specifically, the produced cooling effect is not strong enough since the oil passages 8 available on a single clutch disc 2 are few, and only a very small amount of oil is retained in the oil grooves 9 with their cross-sectional shape progressively smaller toward the radially outer end thereof.
Another conventional clutch disc for use in a wet-type multiplate clutch, as disclosed in Japanese Laid-Open Utility Model Publication No. 54-63850 is illustrated in FIG. 2 of the accompanying drawings. The clutch disc, generally denoted by 20, comprises centrally open disc plate 26 having a plurality of engaging teeth 24 on its outer periphery, with ring shaped frictional members 30 being attached to opposite surfaces of the clutch disc 20. Each of the frictional members 30 has a plurality of radial oil passages 28 defined in one surface thereof at angularly spaced intervals. The clutch disc 20 is rotatable in the direction of the arrow by engagement of the engaging teeth 24 with an outer clutch member (not shown) directly coupled to an engine. When a clutch plate (not shown) is pressed against the clutch disc 20, the clutch disc 20 and the clutch plate are frictionally joined to each other through the frictional member 30 to transmit the drive forces from the engine to a wheel coupled to the clutch plate. Oil 32 is supplied between the clutch disc 20 and the clutch plate. The oil 32 is forced to flow radially outwardly via the radial oil passages 28 under centrifugal forces produced upon rotation of the clutch disc 20. The oil 32 is effective to remove frictional heat by flowing through the oil passages 28, the frictional heat being generated when the clutch disc 20 and the clutch plate are pressed against each other, and also effective to absorb shocks produced when the clutch disc 20 and the companion clutch plate are engaged and disengaged.
The oil passages 28 thus arranged however still fail to make the clutch disc 20 sufficiently durable and also to allow the clutch to be engaged and disengaged sufficiently smoothly.
One proposal to increase the durability of a wet-type clutch disc would be to increase the diameter of a companion clutch plate to obtain an increased contact area. However, an increase in the diameter of the clutch plate would adversely affect the entire design or construction of the body of a two-wheeled vehicle such as a motorcycle in which the clutch is incorporated.